Emulsions are mixtures of at least two immiscible phases comprising a continuous phase and one or more discontinuous phases present as small spheres in the continuous phase.
Often the emulsions are composed of an oil/fat phase and a water phase and optionally a gas phase.
Emulsions are widely used within food industry in products such as butter, spread, dressings and toppings; as well as within the non-food industry in products such as lotions, cremes and ointments.
Even though emulsions inherently are inhomogeneous on the microscopic level it is essential for the perception of the emulsions that they appear homogeneous for the consumer both with respect to the visual appearance and the texture of the product.
For emulsions the properties are to a large extend determined by the size of droplets of the discontinuous phase(s) as well as the distribution. Both the visual appearance as well as properties as viscosity, texture, mouth feel, etc, often referred to as functional properties, is influenced by the size and distribution of the droplets of the discontinuous phase(s).
Because emulsions are composed of at least two immiscible phases there is a risk that an emulsion may break and the two different phases may emerge as visible different components in the product, or that droplets of the discontinuous phase coalesce forming larger droplets with the consequence that the properties of the product changes. Breakdown of an emulsion may appear in different ways depending on the extent of the break down of the emulsion and the properties of the emulsion. Breakdown of the emulsion may appear as streaks having a changed colour in the product, parts of the product having different colour, altered texture of the product or a changed mouth feel of the product. Any of these different appearances of the breaking of the emulsion results in a lower quality product and should therefore be avoided if possible.
In the case of gas being one of the phases in said emulsion, damages may appear as gas droplets of an unacceptable size such as above, e.g., 1 mm across or more.
Because the different phases of the emulsions react differently to changing physical parameters, emulsions are susceptible to influences of physical parameters such as temperature and pressure with the consequence that the visible streaks or areas of the emulsion having changed properties emerge and the product becomes less palatable.
These properties of the emulsions require the process equipment to have little impact on the emulsion after the formation during the manufacture of said emulsions in order to obtain an acceptable product. In particular influence on the emulsions by excessive pressure and temperature have to be avoided.
In U.S. Pat. No. 4,938,660 a screw pump for pumping viscous fluids is described. The pump includes a stator and a rotor lying coaxially with each other and has respective surfaces, which lie seal-tight against each other.
WO 99/19630 and WO 99/19631 disclose screw vacuum pumps where the rotors are provided with a cooling system inside the rotors.
In order to improve the stability of emulsions additives such as emulsifiers are often added to the emulsion, with the consequence that the risk for damaging the emulsion is reduced even though it may not be completely avoided.
Consumers' acceptance of additives, particularly in food products, has declined. Therefore, there is an increasing desire and demand for food products containing low amounts of additives or even completely without additives. This has led to productions of food emulsions, such as dairy products, butter, margarine products, margarine, spread, dressings and toppings containing smaller amounts of emulsifiers, preferably completely without additions of emulsifiers, with the consequence that these products are very susceptible to temperature and pressure influences, which makes them difficult to handle using existing process equipment without damaging the products.
The object of the present invention is to provide new improved screw pumps for susceptible emulsions, which reduce the risk for damaging a susceptible emulsion during pumping.